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XXIII.—On Mirage

Published online by Cambridge University Press:  06 July 2012

Tait
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Extract

I was led to the following investigations while seeking an elementary, and at the same time instructive, application of Hamilton's General Method in Optics. They were completed in all but a few of their numerical details before I met with the remarkable paper by Wollaston, in which the subject of multiple atmospheric images seems first to have been treated by a sound physical method. Wollaston's experiment with a long bar of iron raised to a high temperature suggests undoubtedly the true explanation of at least many of the curious phenomena seen by Vince, Scoresby, and others. But he seems to have thought that sufficient temperature-differences for the natural production of the phenomena could not exist in the atmosphere; and thus the latter part of his paper, in which he tries to explain them by the agency of aqueous vapour, presents a singular contrast to the strength and correctness of the earlier part. A good deal of what follows is implied, if not directly stated, in Wollaston's paper; but I think there is sufficient novelty in what remains to justify my bringing it before the Society.

Type
Research Article
Information
Earth and Environmental Science Transactions of The Royal Society of Edinburgh , Volume 30 , Issue 2 , 1882 , pp. 551 - 578
Copyright
Copyright © Royal Society of Edinburgh 1882

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References

page 551 note * Trans. R.I. A., 1833.

page 551 note ‡ Phil. Trans., 1799.

page 551 note † Phil. Trans., 1800.

page 551 note § Greenland, and Trans. Roy. Soc. Edin., ix. and xi.

page 556 note * When we have . Plotting the curves whose ordinates (in terms of η) are expressed by these two quantities, we find that they touch when b = 3·68a.

page 566 note * B. A. Report, 1862.

page 570 note * B. A. Report, 1870. Thomson finds by a simple process, for the curvature of a ray in a non-homogeneous medium, the expression where n is measured towards the centre of curvature. The result is seen to follow immediately from the corpuscular theory (in which μ = ν) by multiplying both sides by μ 2, for it is thus found to be merely the equation of acceleration of a corpuscle in the direction perpendicular to its path. It is really involved in "Prop. I. of Wollaston's paper (Phil. Trans., 1800).

page 571 note * Mém. de I'Institut, 1809; Récherches sur les Réfractions extraordinaires qui ont lieu près de l'horizon. I presume that my having been altogether ignorant of the existence of this memoir is connected with the fact that it is unintelligible without the plates, and that these were not issued along with it. For in each of the three first libraries which I consulted, that of the Society being one, this volume of the Mém. de I'Institut is devoid of plates. Biot's memoir, however, was issued also as a separate volume, and a copy of this, containing the plates, I procured at last from the Cambridge University Library.

page 576 note * Scoresby's, Arctic. Regions, i. 387 (1820)Google Scholar.

page 577 note * Glaisher's, Travels in the Air, p. 297 (1871)Google Scholar.

page 577 note † Scoresby's, Journal of a Voyage to the Northern Whale Fishery (1823), p. 189Google Scholar.